// © Broadcom. All Rights Reserved.
// The term “Broadcom” refers to Broadcom Inc. and/or its subsidiaries.
// SPDX-License-Identifier: Apache-2.0

package object

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"net/http"
	"os"
	"path"
	"sync"
	"time"

	"github.com/vmware/govmomi/vim25/soap"
)

// DatastoreFile implements io.Reader, io.Seeker and io.Closer interfaces for datastore file access.
type DatastoreFile struct {
	d    Datastore
	ctx  context.Context
	name string

	buf    io.Reader
	body   io.ReadCloser
	length int64
	offset struct {
		read, seek int64
	}
}

// Open opens the named file relative to the Datastore.
func (d Datastore) Open(ctx context.Context, name string) (*DatastoreFile, error) {
	return &DatastoreFile{
		d:      d,
		name:   name,
		length: -1,
		ctx:    ctx,
	}, nil
}

// Read reads up to len(b) bytes from the DatastoreFile.
func (f *DatastoreFile) Read(b []byte) (int, error) {
	if f.offset.read != f.offset.seek {
		// A Seek() call changed the offset, we need to issue a new GET
		_ = f.Close()

		f.offset.read = f.offset.seek
	} else if f.buf != nil {
		// f.buf + f behaves like an io.MultiReader
		n, err := f.buf.Read(b)
		if err == io.EOF {
			f.buf = nil // buffer has been drained
		}
		if n > 0 {
			return n, nil
		}
	}

	body, err := f.get()
	if err != nil {
		return 0, err
	}

	n, err := body.Read(b)

	f.offset.read += int64(n)
	f.offset.seek += int64(n)

	return n, err
}

// Close closes the DatastoreFile.
func (f *DatastoreFile) Close() error {
	var err error

	if f.body != nil {
		err = f.body.Close()
		f.body = nil
	}

	f.buf = nil

	return err
}

// Seek sets the offset for the next Read on the DatastoreFile.
func (f *DatastoreFile) Seek(offset int64, whence int) (int64, error) {
	switch whence {
	case io.SeekStart:
	case io.SeekCurrent:
		offset += f.offset.seek
	case io.SeekEnd:
		if f.length < 0 {
			_, err := f.Stat()
			if err != nil {
				return 0, err
			}
		}
		offset += f.length
	default:
		return 0, errors.New("Seek: invalid whence")
	}

	// allow negative SeekStart for initial Range request
	if offset < 0 {
		return 0, errors.New("Seek: invalid offset")
	}

	f.offset.seek = offset

	return offset, nil
}

type fileStat struct {
	file   *DatastoreFile
	header http.Header
}

func (s *fileStat) Name() string {
	return path.Base(s.file.name)
}

func (s *fileStat) Size() int64 {
	return s.file.length
}

func (s *fileStat) Mode() os.FileMode {
	return 0
}

func (s *fileStat) ModTime() time.Time {
	return time.Now() // no Last-Modified
}

func (s *fileStat) IsDir() bool {
	return false
}

func (s *fileStat) Sys() any {
	return s.header
}

func statusError(res *http.Response) error {
	if res.StatusCode == http.StatusNotFound {
		return os.ErrNotExist
	}
	return errors.New(res.Status)
}

// Stat returns the os.FileInfo interface describing file.
func (f *DatastoreFile) Stat() (os.FileInfo, error) {
	// TODO: consider using Datastore.Stat() instead
	u, p, err := f.d.downloadTicket(f.ctx, f.name, &soap.Download{Method: "HEAD"})
	if err != nil {
		return nil, err
	}

	res, err := f.d.Client().DownloadRequest(f.ctx, u, p)
	if err != nil {
		return nil, err
	}

	if res.StatusCode != http.StatusOK {
		return nil, statusError(res)
	}

	f.length = res.ContentLength

	return &fileStat{f, res.Header}, nil
}

func (f *DatastoreFile) get() (io.Reader, error) {
	if f.body != nil {
		return f.body, nil
	}

	u, p, err := f.d.downloadTicket(f.ctx, f.name, nil)
	if err != nil {
		return nil, err
	}

	if f.offset.read != 0 {
		p.Headers = map[string]string{
			"Range": fmt.Sprintf("bytes=%d-", f.offset.read),
		}
	}

	res, err := f.d.Client().DownloadRequest(f.ctx, u, p)
	if err != nil {
		return nil, err
	}

	switch res.StatusCode {
	case http.StatusOK:
		f.length = res.ContentLength
	case http.StatusPartialContent:
		var start, end int
		cr := res.Header.Get("Content-Range")
		_, err = fmt.Sscanf(cr, "bytes %d-%d/%d", &start, &end, &f.length)
		if err != nil {
			f.length = -1
		}
	case http.StatusRequestedRangeNotSatisfiable:
		// ok: Read() will return io.EOF
	default:
		return nil, statusError(res)
	}

	if f.length < 0 {
		_ = res.Body.Close()
		return nil, errors.New("unable to determine file size")
	}

	f.body = res.Body

	return f.body, nil
}

func lastIndexLines(s []byte, line *int, include func(l int, m string) bool) (int64, bool) {
	i := len(s) - 1
	done := false

	for i > 0 {
		o := bytes.LastIndexByte(s[:i], '\n')
		if o < 0 {
			break
		}

		msg := string(s[o+1 : i+1])
		if !include(*line, msg) {
			done = true
			break
		} else {
			i = o
			*line++
		}
	}

	return int64(i), done
}

// Tail seeks to the position of the last N lines of the file.
func (f *DatastoreFile) Tail(n int) error {
	return f.TailFunc(n, func(line int, _ string) bool { return n > line })
}

// TailFunc will seek backwards in the datastore file until it hits a line that does
// not satisfy the supplied `include` function.
func (f *DatastoreFile) TailFunc(lines int, include func(line int, message string) bool) error {
	// Read the file in reverse using bsize chunks
	const bsize = int64(1024 * 16)

	fsize, err := f.Seek(0, io.SeekEnd)
	if err != nil {
		return err
	}

	if lines == 0 {
		return nil
	}

	chunk := int64(-1)

	buf := bytes.NewBuffer(make([]byte, 0, bsize))
	line := 0

	for {
		var eof bool
		var pos int64

		nread := bsize

		offset := chunk * bsize
		remain := fsize + offset

		if remain < 0 {
			if pos, err = f.Seek(0, io.SeekStart); err != nil {
				return err
			}

			nread = bsize + remain
			eof = true
		} else if pos, err = f.Seek(offset, io.SeekEnd); err != nil {
			return err
		}

		if _, err = io.CopyN(buf, f, nread); err != nil {
			if err != io.EOF {
				return err
			}
		}

		b := buf.Bytes()
		idx, done := lastIndexLines(b, &line, include)

		if done {
			if chunk == -1 {
				// We found all N lines in the last chunk of the file.
				// The seek offset is also now at the current end of file.
				// Save this buffer to avoid another GET request when Read() is called.
				buf.Next(int(idx + 1))
				f.buf = buf
				return nil
			}

			if _, err = f.Seek(pos+idx+1, io.SeekStart); err != nil {
				return err
			}

			break
		}

		if eof {
			if remain < 0 {
				// We found < N lines in the entire file, so seek to the start.
				_, _ = f.Seek(0, io.SeekStart)
			}
			break
		}

		chunk--
		buf.Reset()
	}

	return nil
}

type followDatastoreFile struct {
	r *DatastoreFile
	c chan struct{}
	i time.Duration
	o sync.Once
}

// Read reads up to len(b) bytes from the DatastoreFile being followed.
// This method will block until data is read, an error other than io.EOF is returned or Close() is called.
func (f *followDatastoreFile) Read(p []byte) (int, error) {
	offset := f.r.offset.seek
	stop := false

	for {
		n, err := f.r.Read(p)
		if err != nil && err == io.EOF {
			_ = f.r.Close() // GET request body has been drained.
			if stop {
				return n, err
			}
			err = nil
		}

		if n > 0 {
			return n, err
		}

		select {
		case <-f.c:
			// Wake up and stop polling once the body has been drained
			stop = true
		case <-time.After(f.i):
		}

		info, serr := f.r.Stat()
		if serr != nil {
			// Return EOF rather than 404 if the file goes away
			if serr == os.ErrNotExist {
				_ = f.r.Close()
				return 0, io.EOF
			}
			return 0, serr
		}

		if info.Size() < offset {
			// assume file has be truncated
			offset, err = f.r.Seek(0, io.SeekStart)
			if err != nil {
				return 0, err
			}
		}
	}
}

// Close will stop Follow polling and close the underlying DatastoreFile.
func (f *followDatastoreFile) Close() error {
	f.o.Do(func() { close(f.c) })
	return nil
}

// Follow returns an io.ReadCloser to stream the file contents as data is appended.
func (f *DatastoreFile) Follow(interval time.Duration) io.ReadCloser {
	return &followDatastoreFile{
		r: f,
		c: make(chan struct{}),
		i: interval,
	}
}
